1. Field of Invention
The invention relates to a clamping unit for an injection-molding device for processing thermoplastic, thermosetting or elastomeric material, in which there is arranged between two fixed platens, kept at a distance by means of tie bars, a platen which can be displaced in relation to said fixed platens, part of an injection mold respectively being arranged on one of the fixed platens and on the displaceable platen, it being possible for a force generating element, which generates the clamping force, to be arranged between the one fixed platen and the displaceable platen, and the tie bars being arranged in vertical alignment.
2. Related Prior Art
A clamping unit for an injection-molding machine of this type is known for example from U.S. Pat. No. 4,875,849. The machine described there, for the fabrication of rubber products, is what is known as a vertical machine, i.e. the closing movement of the mold takes place vertically. As a result, an altogether space-saving solution is achieved, since the base area of the machine is relatively small in comparison with horizontal machines, in the case of which a horizontal displacement movement takes place during the opening and closing of the injection mold.
In the case of the aforementioned injection-molding machine according to U.S. Pat. No. 4,875,849, the two-part injection mold is arranged in the upper region of the machine, part of the mold performing said vertical movement during the opening and closing. In order to apply the clamping force for clamping the mold together during the injection of rubber material, a hydraulic piston-cylinder system is arranged in the lower part of the machine. The clamping force required means that the force generating element is of a not inconsiderable size, so that, for ergonomically favorable operation, either the machine has to be arranged in a pit in the floor of the machine shop or the operator has to work on a platform.
To reduce these disadvantages, there are known solutions in which the force generating element for applying the clamping force—usually designed as a hydraulic piston-cylinder system—is not fixedly arranged in the injection-molding machine, but can perform a displacing movement transversely to the closing direction of the mold.
DE-A 18 15 712 discloses an injection-molding machine in which the entire force generating unit can be moved out from the interior of the injection-molding machine, defined by the machine tie bars, perpendicularly to the direction of the closing movement by means of a movement element. This makes it possible during the opening and closing of the mold to perform the required opening stroke of the mold without the force generating unit getting in the way.
A similar solution is disclosed by DE-A 19 12 240, DE-C 1 006 590 and DE 101 00 001 C1.
In the solution of the last-mentioned document, it is provided that, for opening the injection mold, the force generating unit is pivoted out from the interior region of the machine, so that the displaceable platen can move down unhindered.
All these solutions which operate with an extendable force generating unit have disadvantages, which have an effect in particular in the production of molded parts from elastomers on vertical machines:
The extending and retracting of the force generating unit transversely to the closing direction of the mold means that large masses are displaced, which on account of the required production rate of the machine results in mass forces which lead to considerable dynamic problems. Since the moving time of the force generating unit has a direct influence on the cycle time of the machine, and consequently on its productivity, a high degree of sophistication is necessary for the control technology to handle the mass forces, which leads to correspondingly expensive constructions.
Furthermore, said mass forces and the transverse accelerations which act on the force generating unit result in vibrations which are harmful in particular to the sealing systems of the hydraulic components. Therefore, the service life of such systems is shorter than would be the case without vibrations.
It is disadvantageous furthermore that, in solutions of this type, the support of the displaceable platen is restricted to the diameter of the piston of the force generating element, which is negative with regard to the deformation behavior of the mold and the entire machine.
Solutions which operate with an extendable pressure piece in one of the fixed platens have also become known, the pressure piece interacting with a pressure pad which applies the clamping force. Apart from the fact that these are relatively expensive constructions, the operating height which can be achieved with them is still not sufficiently low. Furthermore, the displaceable platen is in this case only supported locally against deflection, so that the mold is not held together with the support over a large area that is in fact desired.